Expansion rivet assemblies are used in various applications, and are particularly well-suited for blind fastening applications commonly found in automobiles. Conventional expansion rivet assemblies include a pin configured to securely engage a grommet or other such body. The pin and body may be molded as two pieces and assembled, or molded as a single piece with a flash joint between the two pieces and driven together in a separate assembly process.
Typically, the pin is driven into the body, which includes ramps on the inside or outside of integrally formed retention legs. The ramps are configured to force the legs to outwardly move or swing when the pin is driven into the body. The solid pin compresses the body legs against a retaining edge of a primary panel.
FIG. 1 illustrates an isometric view of a conventional fastener assembly 10. The fastener assembly 10 includes a pin 12 that is positioned within a body 14. The pin 12 includes a shaft 16 that has a substantially constant axial cross section. For example, the shaft 16 may be cylindrical.
As the pin 12 is driven through a central opening (not shown) formed through the body 14, the shaft encounters ramps (not shown) operatively connected to legs 18 of the body 14. As the pin 12 continues to pass through the body 12 between the legs 18, the shaft 16 engages the ramps, which in turn forces the legs 18 outward. The spreading legs 18 create a fairly robust joint with respect to a panel positioned between the legs 18 and an underside of a collar 20 of the body 14.
Depending on the requirements of the application and joint assembly, a large amount of force may be needed to push the pin 12 into the body 14. The amount of force used to drive the pin into the body depends on the amount of plastic being crushed as the pin 12 and legs 18 interfere with the hole (not shown) in the panel (not shown). If panel separation occurs, the fastener assembly 10 cannot adapt to reform a robust joint. Thus, the joint secured by the fastener assembly 10 may be irreversibly loosened.
Conventional expansion rivet assemblies are not resilient. As such, conventional expansion rivet assemblies may not be able to maintain a robust, tight joint throughout service life. Additionally, in some applications, the force used to drive the pin into the body is so high that a mallet is used to seat the pin to its fully-driven position with respect to the body.
Other types of expansion rivet assemblies include a cored out pin, which acts as a flexible member. Similar to the conventional expansion rivet assemblies explained above, however, these types of assemblies use the pin to drive ramps in order to move the legs of the body outward. Further, the cored out pin may still be difficult to seat with respect to the body.
Thus, a need exists for a fastener assembly that retains a robust, tight joint throughout service life. Additionally, a need exists for a fastener assembly that may be easily secured into a fully-driven position.